netdev - Re: [PATCH net-next 2/8] bpf: introduce BPF_PROG

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Date:   Fri, 2 Feb 2018 07:41:19 -0800
From:   Alexei Starovoitov <ast@...com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>
CC:     Daniel Borkmann <daniel@...earbox.net>, Tejun Heo <tj@...nel.org>,
        David Ahern <dsa@...ulusnetworks.com>,
        <netdev@...r.kernel.org>, <kernel-team@...com>
Subject: Re: [PATCH net-next 2/8] bpf: introduce BPF_PROG_QUERY command

On 2/2/18 6:28 AM, Eric Dumazet wrote:
> On Mon, 2017-10-02 at 16:48 -0700, Alexei Starovoitov wrote:
>> introduce BPF_PROG_QUERY command to retrieve a set of either
>> attached programs to given cgroup or a set of effective programs
>> that will execute for events within a cgroup
>>
>
> ...
>
>> +
>> +int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
>> +				__u32 __user *prog_ids)
>> +{
>> +	struct bpf_prog **prog;
>> +	u32 cnt = 0, id;
>> +
>> +	rcu_read_lock();
>> +	prog = rcu_dereference(progs)->progs;
>> +	for (; *prog; prog++) {
>> +		id = (*prog)->aux->id;
>> +		if (copy_to_user(prog_ids + cnt, &id, sizeof(id))) {
>> +			rcu_read_unlock();
>> +			return -EFAULT;
>> +		}
>> +		cnt++;
>> +	}
>> +	rcu_read_unlock();
>> +	return 0;
>> +}
>
> We can not use copy_to_user() inside rcu_read_lock() section.
>
> CONFIG_DEBUG_ATOMIC_SLEEP=y  would have detected this problem.
>
> Courtesy of syzbot, obviously.

duh. thanks! will fix asap.